I ve never done it but in old and I do mean old car they used copper as a head gasket . You have to google on making a head gasket out of copper and then use the info to temper the copper . I think you could use a copper pipe turn down to the right size or from one out of sheet of copper.
As I said this is just half remembered info about someone doing it themselves.
Life's journey is not to arrive at the grave safely in a well preserved body,but rather to skid in sideways totally worn out shouting WHAT A RUSH, WHAT A RIDE.
"Life is a tragedy when seen in close-up, but a comedy in long-shot." Charlie Chaplin